pid for angle on uwsim

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Hi,

I'm not an expert in control but as far as I know a P controller can reach an stable control depending on the model itself. In my opinion this is happening in your case because of three reasons:

• Drag force helps the control making the system more stable with a force that opposes to the movement.
• There are no perturbation forces as underwater currents are not modeled by default. You can add a node to add perturbation forces and publish them on "/g500/external_force" of type wrenchstamped so it is harder to control.
• IMU has some noise that may add some difficulty to control the vehicle, but it is usually too small to have some impact on the system, you can add some more modifying std tag on XML config file for the IMU.